Method for obtaining alcohols from aldehydes III

ABSTRACT

The present invention relates to a method for preparing saturated Cn- and C2n-alcohols, wherein the ratio of Cn- to C2n-alcohols is controlled by a distillative separation of the aldehydes used.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority pursuant to 35 U.S.C. § 119 to EuropeanPatent Application No. 17205017.0, filed Dec. 1, 2017, which isincorporated herein by reference in its entirety.

FIELD

The present invention relates to a method for preparing C_(n)- andC_(2n)-alcohols, wherein the ratio of C_(n)- to C_(2n)-alcohols iscontrolled by a distillative separation of the aldehydes used.

BACKGROUND

Alcohols fill an important role in industry. They are often used asintermediates for the preparation of lubricant oils, fats, plasticizers,pharmaceuticals, cosmetics and flavourings. Alcohols are also useddirectly as solvents, antifreeze agents or fuel additives.

Plasticizers are used in large amounts for modifying the thermoplasticproperties of numerous industrially important products such as plasticsfor example, but also paints, coating compositions, sealants etc. Animportant class of plasticizers are the ester plasticizers whichinclude, inter alia, phthalic esters, trimellitic esters, phosphoricesters etc. The alcohols used for producing ester plasticizers aregenerally referred to as plasticizer alcohols. To produce esterplasticizers having good performance properties, there is a need forplasticizer alcohols having about 5 to 12 carbon atoms.

Due to the phthalate discussion in the plasticizer sector, the demandfor novel phthalate-free plasticizers is increasing. It is critical inthis case, however, that the respective plasticizers must meet narrowspecifications with regard to their properties with respect to theapplications. Examples here include the viscosity or the volatility ofthe plasticizers. Control of the essential properties of theplasticizers depends in this case less on the esterification reactiontypically used in the production of plasticizers but rather on the rawmaterials used, especially the alcohols used. Essential factors hereare, for example, the number of carbon atoms of the alcohols used or theisomer distribution thereof. For this purpose, alcohols having 4, 5 or 6carbon atoms for example are suitable. At the same time, however, it isalso necessary to produce the C8-, C10- and C12-alcohols described.

One of the best-known routes to alcohols is the hydroformylationreaction in which alkenes are converted to aldehydes, which are thensubjected to a hydrogenation, in order to produce the correspondingalcohols (C_(n)-alcohols). An exception here is the hydroformylation ofpropene and unbranched butenes. Here, the resulting aldehydes areusually subjected to a further reaction step, the aldolization, in orderto produce long-chain unsaturated aldehydes. These are then alsosubjected to a hydrogenation and the longer-chain alcohols(C2n-alcohols) obtained are used for the most part in the production ofphthalate-containing plasticizers.

For instance, EP 1004563 describes the preparation of alcohols byhydroformylation of an olefin, aldol condensation of a portion of thealdehyde and subsequent hydrogenation reaction. However, specificcontrol of the composition of the alcohols obtained is not possible inthis manner.

The challenge that arises therefrom is on the one hand to control theisomer distribution of the alcohols to be produced, and on the otherhand however also to control especially the ratio of C_(n)- toC_(2n)-alcohols.

SUMMARY

The object of the present invention is to provide a method which meetsthe requirements mentioned above and allows the selective control of thecomposition of the resulting alcohols.

The object of the present invention is achieved by a method forpreparing C_(n)- and C_(2n)-alcohols, wherein the ratio of C_(n)- toC_(2n)-alcohols is determined by selective control of the reactantstreams of aldolization and hydrogenation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a method according to one or more embodimentsdescribed herein.

FIG. 2 is a schematic of a method according to one or more embodimentsdescribed herein.

FIG. 3 is a schematic of a method according to one or more embodimentsdescribed herein.

FIG. 4 is a schematic of a method according to one or more embodimentsdescribed herein.

DETAILED DESCRIPTION

Accordingly, the present invention relates to a method for preparingsaturated C_(n)- and C_(2n)-alcohols where n=4, 5 and 6 comprising themethod steps of

-   -   a) providing a mixture of isomeric C_(n)-aldehydes where n=4, 5        and 6, wherein the proportion of unbranched aldehydes is at        least 20% by weight, based on the C_(n)-aldehydes provided where        n=4, 5 and 6,    -   b) carrying out a distillation for the at least partial        separation of the isomeric C_(n) aldehydes where n=4, 5 and 6        into a first stream having a higher proportion of linear        aldehydes than the mixture provided in a) and into a second        stream having a higher proportion of branched aldehydes than the        mixture provided in a)    -   c) carrying out an aldol condensation of the aldehydes present        in the first stream having a higher proportion of linear        aldehydes than the mixture provided in a) to obtain a mixture of        C_(n)- and α,β-unsaturated C_(2n)-aldehydes    -   d) mixing the mixture of C_(n)- and α,β-unsaturated        C_(2n)-aldehydes obtained in c) with the second stream, provided        in b), having a higher proportion of branched Cn aldehydes where        n=4, 5 and 6 than the mixture provided in a)    -   e) hydrogenating the mixture of C_(n)- and α,β-unsaturated        C_(2n)-aldehydes and C_(n)-aldehydes where n=4, 5 and 6 obtained        in d) with hydrogen to obtain a mixture of saturated C_(n) and        C_(2n)-alcohols and    -   f) separating the mixture of C_(n) and C_(2n)-alcohols.

The process chain according to the invention allows, in a surprisingmanner, the preparation of saturated C_(n) and C_(2n)-alcohols which maybe used directly for the production of plasticizers. It has been foundparticularly in this case that the isomer distribution, for example ofthe C_(n)-alcohols, is such that these result in plasticizers afteresterification which have an advantageous spectrum of properties and thewater content of the Cn alcohols is so low that these can be usedwithout further pretreatment in anhydride esterification reactions ortransesterifications.

The basic sequence of the method according to the invention is shown inFIG. 1. In the first step, a stream composed of isomeric C_(n)-aldehydeswhere n=4, 5 and 6 is provided (1) and is separated distillatively intoa first stream (1 a) having a higher proportion of linear aldehydes thanthe mixture provided in a) and into a second stream (1 b) having ahigher proportion of branched aldehydes than the mixture provided in a).The first stream (1 a) comprising isomeric C_(n)-aldehydes where n=4, 5and 6 having a higher proportion of linear aldehydes is introduced intoa reactor for the purpose of carrying out an aldol condensation toobtain a mixture of C_(n)- and α,β-unsaturated C_(2n)-aldehydes. Theproduct stream obtained from the aldol condensation comprising a mixtureof C_(n)- and α,β-unsaturated C_(2n)-aldehydes is mixed with the stream(1 b) obtained in the context of distillative separation comprisingisomeric C_(n)-aldehydes where n=4, 5 and 6 having a higher proportionof branched aldehydes and is transferred as reactant stream (2) into afurther reactor for the purpose of carrying out a hydrogenation of themixture of C_(n)- and α,β-unsaturated C_(2n)-aldehydes and isomericC_(n)-aldehydes where n=4, 5 and 6 (reactant stream (2)) with hydrogento obtain a mixture of saturated C_(n) and C_(2n)-alcohols. Therespective fractions with Cn and C2n alcohols as main components areobtained from this mixture by thermal separation.

In principle, all C_(n)-aldehydes where n=4, 5 and 6 known to thoseskilled in the art are suitable, either in pure form or in the form ofmixtures, for use in the method according to the present invention,wherein a basic prerequisite is that the proportion of unbranchedaldehydes is at least 20% by weight, based on the C_(n)-aldehydes usedwhere n=4, 5 and 6.

In particular in the method according to the invention, aldehyde streamsof identical chain length are used. The proportion of unbranchedaldehydes is at least 20% by weight, based on the C_(n)-aldehydes usedwhere n=4, 5 and 6, preferably at least 40% by weight. In particular,the proportion of unbranched aldehydes is 40 to 99.5% by weight,especially preferably the proportion of unbranched aldehydes is 95-99.5%by weight, based on the C_(n)-aldehydes used where n=4, 5 and 6.

In the context of industrial scale processes, many such aldehydes ormixtures thereof are obtained from the corresponding olefins byhydroformylation.

Accordingly, in a preferred embodiment of the present invention, theC_(n)-aldehydes where n=4, 5 and 6 provided in step a) are prepared byhydroformylation of isomeric olefins having 3 to 5 carbon atoms withsynthesis gas in the presence of a hydroformylation catalyst to form thealdehydes specified. Appropriate hydroformylation methods are known tothose skilled in the art and are described by way of example inHydroformylation Fundamentals, Processes and Applications in OrganicSynthesis Volume 1 & 2 Edition 1, Franke, Borner, Willey VCH Verlag GmbH& Co.

Generally, the process is operated with rhodium or cobalt catalysts andalso with or without complex-stabilizing additives such as organicphosphines or phosphites. The temperatures and pressures may be variedwithin wide limits depending on the catalyst or olefin. A description ofthe hydroformylation of olefins is found for example in J. Falbe, NewSyntheses with Carbon Monoxide, Springer-Verlag, Heidelberg-New York,1980, pages 99 ff. and in Kirk-Othmer, Encyclopedia of ChemicalTechnology, Volume 17, 4th Edition, John Wiley & Sons, pages 902 to 919(1996).

The reaction mixtures of the hydroformylation are advantageously firstlyfreed from the catalyst prior to use in the method according to theinvention. If a cobalt catalyst has been used, this can be accomplishedby releasing pressure, oxidation of the cobalt carbonyl compoundsremaining in the hydroformylation mixture in the presence of water oraqueous acid and removal of the aqueous phase. Decobalting processes arewell known, see for example J. Falbe, loc. cit., Kirk-Othmer, loc. cit.,164, 175, BASF-Verfahren.

If a rhodium compound is used as hydroformylation catalyst, it can beremoved, for example, by thin-film evaporation as distillation residue.

In the preferred embodiment of the present invention, thehydroformylation is carried out according to the method described in WO2017/080690.

In this case, in the hydroformylation a catalyst system is used whichcomprises rhodium as central atom and is complexed with the ligand (1):

The IUPAC designation for ligand (1) is3,3′-di-tert-butyl-5,5′-dimethoxy-[1,1′-biphenyl]-2,2′-diyItetrakis(2,4-dimethylphenyl)bis(phosphite).

The hydroformylation is effected in particular ata temperature between120° C. and 140° C. The pressure is preferably between 15*10⁵ Pa and25*10⁵ Pa.

To increase operating duration, the hydroformylation is performed in thepresence of an organic amine of formula (2)

in which Ra, Rb, Rc, Rd, Re and Rf represent identical or differenthydrocarbon radicals which may also be bonded to one another. Theorganic amine preferably comprises at least one2,2,6,6-tetramethylpiperidine unit. Specifically the organic amine maybe a di-4-(2,2,6,6-tetramethylpiperidinyl) sebacate.

It is recommended to establish a rhodium concentration in the firstreaction mixture between 1 ppmw and 1000 ppmw. The ligand/rhodium ratioshould be between 1:1 to 100:1 and no further ligand is to be providedas part of the homogeneous catalyst system in addition to theorganophosphorus compound according to formula (1). In industrialoperation it cannot be ruled out that owing to impuritiesorganophosphorus compounds other than3,3′-di-tert-butyl-5,5′-dimethoxy-[1,1′-biphenyl]-2,2′-diyItetrakis(2,4-dimethylphenyl)bis(phosphite)complex to the rhodium as part of the catalyst system. However, suchimpurities can be disregarded at the indicated ligand/rhodium ratio.This statement relates solely to ligand (1) and no further ligand needbe intentionally provided.

The isomeric C_(n)-aldehydes used in the method according to theinvention where n=4, 5 and 6 are separated at least partially by meansof a distillation of the isomeric Cn aldehydes where n=4, 5 and 6according to step b) into a first stream (1 a) having a higherproportion of linear aldehydes than the mixture provided in a) and intoa second stream (1 b) having a higher proportion of branched aldehydesthan the mixture provided in a).

The stream is divided via a rectification column. This is effectedaccording to the prior art and separates the feed (1) into the twoindividual streams (1 a) and (1 b).

The ratios between (1 a) and (1 b) are selected such that the desiredamount of C_(2n) alcohol and C_(n) alcohol of the desired isomerdistribution are formed according to the following approach:Mass stream C _(2n)alcohol(5)=Feed*Split*(Xn_Aldol*FeedS_w_n+Xi_Aldol*FeedS_w_i)*(2*M_Cn_al−18)/(2*M_Cn_al+2)*X_Hydr*X_DistMass streamCnalcohol(4)=Feed*Split*((1−Xn_Aldol)*FeedS_w_n)+Feed*(1−Split)*FeedD_w_n/M_Cn_al*M_Cn_ol*X_n_Hydr*X_n_Dist+Feed*Split*((1−Xi_Aldol)*FeedS_w_i)+Feed*(1−Split)*FeedD_w_i/M_Cn_al*M_Cn_ol*X_i_Hydr*X_i_DistMass stream(1b)=Feed*(1−Split)Proportion of linearalcohols(4)=Feed*Split*((1−Xn_Aldol)*FeedS_w_n)+Feed*(1−Split)*FeedD_w_n/M_Cn_al*M_Cn_ol*X_n_Hydr*X_n_Disti(Feed*Split*((1−Xn_Aldol)*FeedS_w_n)+Feed*(1−Split)*FeedD_w_n/M_Cn_al*M_Cn_ol*X_n_Hydr*X_n_Dist+Feed*Split*((1−Xi_Aldol)*FeedS_w_i)+Feed*(1−Split)*FeedD_w_i/M_Cn_al*M_Cn_ol*X_i_Hydr*X_i_Dist)Feed=feed (1)Split=percentage proportion (1 a) based on feed (1)FeedS_w_n=percentage concentration of linear aldehydes Cn in stream (1a)FeedS_w_i=percentage concentration of branched aldehydes Cn in stream (1a)FeedD_w_n=percentage concentration of linear aldehydes Cn in stream (1b)FeedD_w_i=percentage concentration of branched aldehydes Cn in stream (1b)Xn_Aldol=yield of C2n aldolization product based on the linear aldehydesCn in the aldolization (B)Xi_Aldol=yield of C2n aldolization product based on the branchedaldehydes Cn of the aldolization (B)M_Cn_al=molar mass of the aldehydes CnX_Hydr=yield of C2n aldolization products hydrogenated to thecorresponding alcoholsX_Dist=yield of C2n alcohols in the distillationX_n_Hydr=yield of linear Cn aldehydes hydrogenated to the correspondingalcoholsX_i_Hydr=yield of branched Cn aldehydes hydrogenated to thecorresponding alcoholsX_n_Dist=yield of linear Cn alcohols in the distillationX_i_Dist=yield of branched Cn alcohols in the distillation

The isomer distribution of the C_(n) alcohols can still be shiftedwithin limits by the use of thermal separation. For this purpose, thefollowing applies for controlling the amount, based only on the adjustedmass streams of C_(n) alcohol.M_Dist=−1*(M_Feed*(Prod_w_n−Feed_w_n)/(Dist_w_n−Prod_w_n))

In this case the following limits applyDist_w_n<Feed_w_n<Prod_w_nM_Feed=mass stream of Cn alcoholsProd_w_n=percentage concentration of linear aldehydes Cn of product ((4)in FIGS. 2&3))Feed_w_n=percentage concentration of linear aldehydes Cn of feed ((8) inFIGS. 2&3))Dist_w_n=percentage concentration of linear aldehydes Cn of distillate((10) in FIGS. 2&3))M_Dist=mass stream of Cn alcohols to be discharged ((10) in FIGS. 2&3))

All positions refer only to the alcohol components; secondary componentsare not considered and are subtracted from the mass streams.

In accordance with the invention, the isomeric C_(n)-aldehydes wheren=4, 5 and 6 in stream (1 a) are converted by aldol condensation,particularly in the presence of aqueous sodium hydroxide solution, to amixture of C_(n)- and α,β-unsaturated C_(2n)-aldehydes. Appropriateprocesses are known, for example, from DE19957522A1, DE102009045139A1,DE102009001594A1.

The aldol condensation is particularly preferably carried out in atubular reactor which comprises at least one mixing module whichdisperses the reactant aldehyde into droplets having an average diameter(Sauter diameter) of 0.2 mm to 2 mm in the continuous catalyst phase(process liquor), which consists of aqueous sodium hydroxide solutionand sodium salts of carboxylic acids and has a sodium content of 0.6 to1.75% by mass and a pH in the range from 12.5 to 13.5.

To form the process liquor, aqueous sodium hydroxide solution is used inthe method according to the invention. The aqueous sodium hydroxidesolution forms the process liquor together wih the return liquor. Thereturn liquor comprises, as well as sodium hydroxide, sodium salts ofcarboxylic acids, principally of pentanoic acids. The carboxylic acidsalts have been formed essentially by the Cannizzaro reaction.

In the method according to the invention, the sodium content of theprocess liquor at the reactor inlet is 0.60 to 1.75% by mass, especially1.1 to 1.20% by mass. To adjust the sodium concentration of the processliquor, aqueous sodium hydroxide solution is fed into the return liquorat a concentration greater than 2.5% by mass. In order to introducelittle water into the reaction system, preference is given to usingaqueous sodium hydroxide solution at a relatively high concentration. Inthe method according to the invention, preference is given to usingaqueous sodium hydroxide solution in the concentration range from 5 to30% by mass, for example at 10% by mass.

The method according to the invention is performed in a tubular reactorwhich has at least one mixing module, preferably more than one mixingmodule. In particular, the number of mixing modules is 1 to 30, veryparticularly 10 to 20.

A mixing module means a static mixer, i.e. a passive component which hasno direct intrinsic energy requirement.

The tubular reactor consists of a tube which is preferably alignedvertically. The flow through it may be from bottom to top or vice versa.An industrial reactor may also consist of a plurality of tubes arrangedin parallel, which are connected to one another by U-tubes.

A mixing module is preferably present at the reactor inlet. Voids arepresent between the mixing modules. The proportion by volume of thetotal volume of the reactor outside the mixing module(s) is 20 to 80%,especially 30 to 60%. The mixing modules may have equal or differentdistances from one another. The distance between the mixer modulespreferably decreases in the direction of flow. The distances of themixer modules from one another are, depending on the intendedsuperficial velocity, the phase ratio between reactant and catalystphases, the reaction progress and the mixer type, 0.2 to five times themixing module length, especially 0.5 to two times the mixing modulelength.

The mixing module consists of a static mixer or of an arrangement of twoor more, preferably two, static mixers.

When the mixer module consists of two identical static mixers, these arepreferably arranged twisted about the longitudinal axis of the reactor,especially twisted by an angle of 45° up to 90°. Mixing elements arepreferably arranged in the mixer module at a distance of two tubediameters.

A mixing module may also consist of static mixers of different design.It may be advantageous that, in the case of a mixer module consisting oftwo static mixers, the first has a lower hydraulic diameter than thesecond. In this case, the first static mixer produces very smalldroplets and the second static mixer, as a result of selection of agreater hydraulic diameter, prevents the coalescence of the cluster ofdroplets.

The hydraulic diameter of the mixing elements of the mixer modulespreferably decreases in the direction of flow.

The mixer modules may be the same or different in the reactor, i.e. theymay be of the same or different design.

The mixing elements used may be all static mixers which, under theintended reaction conditions, are capable of dispersing the organicphase in the catalyst phase into droplets with an average Sauterdiameter in the range from 0.2 to 2.0 mm.

The static mixers used in the method according to the invention may bemixing elements which are suitable for the dispersion of two immisciblelow-viscosity liquids, as are commercially available. In accordance withthe invention, the aldol condensation of the C_(n)-aldehydes is carriedout in the temperature range from 100 to 150° C., more particularly inthe range from 110 to 140° C., especially preferably in the range from120 to 140° C.

The reaction may be carried out isothermally, adiabatically orpolytropically in the temperature ranges specified. For example, thetemperature at the reactor inlet may be 120° C. and the temperature atthe reactor outlet may be 140° C.

The reaction pressure in the reactor is at least high enough so thatboth the process liquor and the organic substances (reactant andproducts) are each present as a liquid phase. The pressure is in therange from 0.2 to 1.0 MPa, preferably in the range from 0.3 to 0.5 MPa.

In the method according to the invention, the ratio [kg/kg] of processliquor to reactant at the reactor inlet is in the range from 5 to 40,especially in the range from 10 to 15.

The average superficial velocity of the mixture of reactant and processliquor (assuming the same flow rate of both phases) in the industrialreactor is in the range from 0.5 to 4 m/s, especially in the range from1 to 2.5 m/s.

The average residence time of the reaction mixture in the reactor is 40to 360 s, especially 60 to 180 s.

In the method according to the invention, the droplets of the organicphase dispersed in the process liquor on leaving a mixer module have anaverage Sauter diameter of 0.2 to 2 mm, especially of 0.6 to 1.3 mm.

The load factor is in the range from 0.2 to 0.8.

The aldehydes obtained may optionally be processed prior to further usein the method according to the invention.

One way of doing so is to cool the reaction output and to separate theorganic phase from the liquor phase. The phase separation is preferablyeffected in the temperature range from 60 to 130° C., particularly inthe range from 70 to 120° C., very particularly in the range from 90 to110° C. The separation times, depending on the temperature selected, are3 to 10 minutes. At temperatures above 90° C., the separation time isless than 8 minutes. The separation time is defined as the time by whichthe organic product of value phase is clear and free of traces ofheterogeneous water.

To separate the heavy, aqueous phase from the light organic phase,separators may be used which facilitate the phase separation usinggravity alone. These so-called gravity separators may also be providedwith internals as a coalescence-promoting measure to improve theseparating performance. The use of internals accelerates the coalescenceand sedimentation process. As coalescence aids, it is possible to use,for example, plates, random packings, mesh packings or fibre bedseparators. Gravity separators can be configured as horizontal vesselsor as upright vessels.

As an alternative to gravity separators, it is also possible to useseparators operating according to the centrifugal principle forliquid-liquid separation. The heavy phase here is separated off by meansof centrifugal forces in a rotating drum.

In order to separate off the heavy, aqueous phase in the methodaccording to the invention, preference is given to using gravityseparators, preferably gravity separators configured as horizontalvessels with internals.

Part of the liquor phase which has been separated off is discharged toremove water of reaction, and the other part is recirculated into thereactor. With the discharge stream, a portion of the carboxylic acidsformed as by-products (as sodium salts) and sodium hydroxide are alsoremoved. This stream can be sent to a wastewater treatment plant.However, it is also possible to work up this stream and partlyrecirculate it into the process, as described, for example, in DE 198 49922 and DE 198 49 924.

If the organic phase, in addition to the C_(n)- and α,β-unsaturatedC_(2n)-aldehydes, comprises other by-products such as carboxylic acidsalts, sodium hydroxide and dissolved water, traces of base and aportion of the carboxylic acid salts can be removed by water scrubbing.The water extract obtained can be used to make up fresh base.

The C_(n)- and α,β-unsaturated C_(2n)-aldehydes thus obtained are mixedaccording to step d) with the second stream (1 b) obtained in b), havinga higher proportion of branched aldehydes than the mixture provided ina), to obtain a reactant stream (2).

The mixing of the two substreams is ensured by appropriate static ordynamic mixers, as is known to those skilled in the art. The two streamsare preferably combined here by means of a static mixer such as, forexample, the CompaX™ module from Sulzer. At this position, anappropriate pump may also serve as dynamic mixer.

The reactant stream (2) obtained by mixing comprises the C_(n)- andα,β-unsaturated C_(2n)-aldehydes obtained in the aldolization and thefraction obtained distillatively in step b) comprising C_(n)-aldehydeswhere n=4, 5 and 6 having a higher proportion of branched aldehydes thanthe starting mixture in the form of a mixture. This mixture ishydrogenated with hydrogen according to step e) of the method accordingto the invention to obtain a mixture of saturated C_(n) andC_(2n)-alcohols. The hydrogenation is likewise effected according toprocesses known per se, for example in the temperature range from 170°C. to 200° C. at a pressure of 15*10⁵ Pa to 30*10⁵ Pa over a supportedcatalyst which contains at least nickel and copper as active components,as known for example from EP3037400.

The hydrogenation catalyst preferably consists of a support materialbased on titanium dioxide, zirconium dioxide, aluminium oxide, siliconoxide or mixtures thereof, wherein hydrogenation-active metals, inparticular at least one element from the group of copper, cobalt,nickel, chromium, are applied to this support material.

It is possible to use aluminium oxide, aluminosilicate, silicon dioxide,titanium dioxide, zirconium dioxide as support precursors. A preferredsupport precursor is aluminium oxide, especially γ-aluminium oxide. Thecatalyst may contain one or more of the hydrogenation-active metals.

The catalyst according to the invention preferably contains the metalscopper, chromium, nickel. The catalyst particularly preferably containsthe combination of the three metals copper, chromium and nickel ashydrogenation-active metal.

The total content of hydrogenation-active metals, based on the reducedcatalyst, is in the range from 1 to 40% by mass, especially in the rangefrom 5 to 25% by mass, calculated as the metal.

The catalysts according to the invention are prepared advantageously ina form which produces low flow resistance in the hydrogenation, such asfor example tablets, cylinders, strand extrudates or rings. In thecourse of preparation of the catalyst, the preliminary support materialis typically made into the appropriate form. Moulded preliminary supportmaterial is also commercially available.

In the method according to the invention, the hydrogenation can becarried out continuously or batchwise over finely divided or mouldedcatalysts arranged suspended in the fixed bed. Preference is given tocontinuous hydrogenation over a catalyst arranged in the fixed bed inwhich the product/reactant phase is mainly in the liquid state under thereaction conditions.

If the hydrogenation is carried out continuously over a catalystarranged in the fixed bed, it is advantageous to convert the catalyst tothe active form prior to the hydrogenation. This can be effected byreduction of the catalyst using hydrogen-containing gases according to atemperature programme. In this case, the reduction may be carried outoptionally in the presence of a liquid phase which is passed over thecatalyst, such as described, for example, in DE 199 33 348.

The hydrogenation method according to the invention is carried out inthe trickle phase or preferably in the liquid phase in triphase reactorsin cocurrent, wherein the hydrogen is finely distributed in a mannerknown per se in the liquid reactant/product stream. In the interests ofa uniform liquid distribution, of improved removal of heat of reactionand of a high space-time yield, the reactors are preferably operatedwith high liquid loadings of 15 to 120, especially of 25 to 80 m³ per m²of cross section of the empty reactor and per hour. When a reactor isoperated isothermally and in straight pass, the specific liquid hourlyspace velocity (LHSV) may assume values between 0.1 and 10 h⁻¹.

The method according to the invention is carried out with hydrogen in apressure range from 5 to 100 bar, preferably between 5 and 40 bar,particularly preferably in the range from 10 to 25 bar. Thehydrogenation temperatures are between 120 and 220° C., especiallybetween 140 and 190° C.

The hydrogen used for the hydrogenation may contain inert gases such asmethane or nitrogen for example. Preference is given to using hydrogenhaving a purity of greater than 98%, especially greater than 99%.

For the method according to the invention, various method variants maybe selected. The method can be carried out single-stage or multistage,adiabatically or practically isothermally, i.e. with a temperatureincrease of less than 10° C. In the latter case, all reactors,advantageously tubular reactors, may be operated adiabatically orpractically isothermally and also one or more adiabatically and theothers practically isothermally. It is also possible to hydrogenate thecarbonyl compounds or mixtures of carbonyl compounds in the presence ofwater in straight pass or with product recycling.

In addition to the α,β-unsaturated C_(2n)-aldehydes and the unreactedC_(n) starting aldehydes in the aldolization, the hydrogenation alsoconverts the C_(n) aldehydes having a higher proportion of branchedaldehydes present in the second stream (1 b) to the correspondingalcohols.

According to the invention, the separation of the mixture of saturatedC_(n) and C_(2n) alcohols follows on from the hydrogenation according tostep f), in which in this case the separation of the C_(n)-alcohols andthe C_(2n)-alcohols may be effected by various combinations of classicaldistillation columns or dividing wall columns, or a combination of bothcolumn types, by means of at least one two-column system or by means ofat least one dividing wall column.

In a particularly preferred embodiment of the present invention, atwo-column system or a dividing wall column is used in order in bothcases to obtain the C_(n)- and C_(2n)-alcohols as products of value.

The various method variants are described in more detail below.

In one embodiment of the present invention, at least one two-columnsystem is used. In the first column, in the course of the method,alkanes formed (in the case of butenes mainly nonane), together with theC_(n)-alcohol (for example 2-methylbutanol) and water, are taken via theoverhead. Phase separation takes place there and the organic phase isfed again to the column as return stream. By means of this azeotropedrying, the water content in the bottoms is obtained at less than 1000ppm. In the second column, the C_(n) alcohol is taken via the overheadand thus separated from the high boilers. By means of appropriate modeof operation of the column, the isomeric composition of the C5 alcoholsmay additionally be controlled.

FIG. 2 shows the detailed sequence of the separation of the mixture ofC_(n) and C_(2n)-alcohols by means of a two-column system which issubdivided into the following substeps:

-   I. Distillative separation (G) of the crude product stream of the    hydrogenation (3) from step e) into a low-boiler stream (6) and a    high-boiler stream (15). In this case, the low-boiler stream (6)    comprises as main product the alcohols of the starting aldehydes and    further substances or azeotropes having a lower boiling point than    the alcohols formed from the α,β-unsaturated C_(2n)-aldehydes and    heterogeneous water. The high-boiler stream (15) comprises as main    product the alcohols formed from the α,β-unsaturated    C_(2n)-aldehydes and high-boilers or azeotropes having a higher    boiling point than the C_(2n)-alcohols.-   II. Removal of the heterogeneous water (7) from the distillate    fraction (6) via separator (F).-   III. Distillative separation (H) of the organic phase (8) from F    into a low-boiler stream (9) and a high-boiler stream (12). The    low-boiler stream (9) comprises substances or azeotropes having a    lower boiling point than the highest boiling C_(n)-alcohol and may    contain heterogeneous water (11) after condensation. The high-boiler    stream mainly comprises the C_(n)-alcohols and substances or    azeotropes having a higher boiling point than the highest boiling    C_(n)-alcohol.-   IV. Removal of the heterogeneous water (11) by phase separation (E).    The organic phase is fed again as return stream (19) to column (H).    A portion of the organic phase (10) obtained is driven from the    system.-   V. Distillative separation (I) of the high-boiler stream (12) into a    low-boiler stream (4) and a high-boiler stream (14). The low-boiler    stream (4) mainly comprises the C_(n)-alcohol with the desired    isomer distribution. The high-boiler stream (14) mainly comprises    substances or azeotropes having a higher boiling point than the    highest boiling C_(n)-alcohol.-   VI. Distillative separation of the high-boiler stream (15) into a    low-boiler stream (5), which comprises the C_(2n)-alcohols, and a    high-boiler stream (18). The low-boiler stream (5) mainly comprises    the C_(2n)-alcohol. The high-boiler stream (18) mainly comprises    substances or azeotropes having a higher boiling point than the    highest boiling C_(2n)-alcohol.

The temperature profiles used in the columns are adjusted in each casedepending on the respective composition of the product stream from thehydrogenation (step b) of the method according to the invention.

For example, the product stream (3) may have the following composition:

2-Propylheptenal (% by mass) 0.9 n-Pentanol (% by mass) 2.82-Methylbutanol (% by mass) 2.8 2-Propylheptanol (% by mass) 87.52-Propyl-4-methylhexanol (% by mass) 4.2 H₂O 1.7

In the case of this composition, column (G) is operated preferably at atop pressure of 0.2 bar(abs) and a pressure drop of 0.1 bar, and abottom temperature of 176° C. and a top temperature of 65° C. are to bemaintained, or corresponding equivalents. Column (H) is operatedparticularly at a top pressure of 1.05 bar(abs) and a pressure drop of0.03 bar at a bottom temperature of 137° C. and a top temperature of 94°C., or corresponding equivalents. Column (I) is generally to bemaintained at a top pressure of 1.08 bar(abs) and a pressure differenceof 0.03 bar at a bottom temperature of 178° C. and a top temperature of134° C., or corresponding equivalents.

Column (J) is operated ata pressure of 0.15 bar(abs) and a pressuredifference of 0.006 bar at a bottom temperature of 175° C. and a toptemperature of 158° C., or corresponding equivalents. The temperatureprofiles specified are to be considered as exemplary. Furtherconfigurations, especially in connection with varying feed compositions,are included in the context of the present invention.

In a further likewise preferred embodiment of the present invention, atleast one dividing wall column is used. In a dividing wall column, theseparating operations described for the two-column system can becombined in one column. The example of alkane/2-methylbutanol/watermixture is also obtained via the overhead, is subjected to an analogousphase separation and the organic phase is fed back again to the columnas return stream. Via a side take-off in the region of the dividingwall, the Co-alcohol that meets the specification is drawn off. Theisomer ratio of the Co-alcohol in the side take-off may be controlledwithin certain limits via the reduction in the distillate of the organicphase and the proportion of alcohol in the bottom of the column. FIG. 3depicts the sequence when using a dividing wall column (K) forseparating the low-boiler stream (6).

In this context, the columns H and I depicted in FIG. 2 are combined toform a dividing wall column (K) (see FIG. 3). The dividing wall column(K) is to be maintained at a top pressure of 1.05 bar(abs) and apressure drop of 0.06 bar, a bottom temperature of 180° C., a toptemperature of 118° C. and a product temperature of 134° C., orcorresponding equivalents.

FIG. 4 shows a further preferred embodiment, in which the separation ofthe crude product stream from the hydrogenation e) is also achieved by adividing wall column. In this case, the C_(2n)-alcohol is drawn off viaa side take-off in the region of the dividing wall.

The method according to the invention is suitable in an advantageousmanner for the production of C_(n)- and C_(2n)-alcohols from aldehydesand in the case of upstream hydroformylation from olefins.

In the case of the isomeric C_(n)-aldehydes used where n=4, 5 and 6, n=5is especially preferred. As already discussed above, such aldehydes maybe obtained by hydroformylation of corresponding isomeric olefins. Inthe latter case, these are particularly olefins having 3 to 5 carbonatoms, namely propenes, butenes and pentenes, wherein the respectivepositional isomers (in the case of butenes and pentenes) are included bymeans of the designations specified. The isomeric olefins areparticularly preferably butenes. In the latter case, these are convertedby the method according to the invention to pentanol mixtures anddecanol mixtures.

With regard to plasticizer syntheses, the isomer distributions of thepentanol mixtures are of particular interest.

By way of example and as a preferred embodiment, the pentanol mixtureobtained preferably comprises less than 60 mol % n-pentanol. The minimumcontent of n-pentanol in the mixture of isomeric pentanols is preferablyat least 2 mol %, preferably at least 10 mol %, more preferably morethan 20 mol %, with more preference more than 22.5 mol % or even morethan 25 mol %, more preferably more than 27.5 mol %, 30 mol % or evenmore than 35 mol %. In addition to the linear n-pentyl radicals,particular preference is given to pentanols comprising branched pentylradicals. A branched pentyl radical is preferably a methylbutyl radical.Accordingly, preference is given to a pentanol mixture in which thebranched pentyl radicals consist of methylbutyl radicals to an extent ofat least 50 mol %, preferably to an extent of at least 60 mol %, furtherpreferably to an extent of at least 70 mol %, still further preferablyto an extent of at least 80 mol %, even more preferably to an extent ofat least 90 mol % and especially to an extent of at least 95 mol %.

It is advantageous if the branched isomeric pentyl radicals have a largeproportion of 2-methylbutyl radicals. In a preferred embodiment,therefore, at least 50 mol %, preferably at least 60 mol %, morepreferably at least 70 mol %, further preferably at least 80 mol %,especially preferably at least 90 mol % and especially at least 95 mol %of the branched isomeric pentyl radicals are 2-methylbutyl radicals. Thepreferred pentanol mixtures preferably comprise 20 to 95 mol %,preferably 30 to 85 mol % and especially 40 to 75 mol % of 2-methylbutylradicals, based on all pentyl radicals present.

In a particularly preferred embodiment, the pentanol mixture consists toan extent of at least 75 mol %, more preferably to an extent of at least90 mol % and especially to an extent of at least 95 mol % of pentanolscomprising—preferably exclusively—2-methylbutyl and/or linear pentylradicals, where the molar ratio of 2-methylbutyl radicals to linearpentyl radicals in this pentanol mixture is preferably in the range from99:1 to 40:60, especially in the range from 70:30 to 40:60.

The desired product properties, especially the isomer distributionsmentioned above, are adjusted particularly by the partial isomerseparation of the aldehydes described in method step b) by means ofdistillation and by the parameters for carrying out the separation ofthe mixture of C_(n) and C_(2n)-alcohols by the two-column or dividingwall column systems used specified in step f).

Even without further elaboration it is believed that a person skilled inthe art will be able to make the widest use of the above description.The preferred embodiments and examples are therefore to be interpretedmerely as a descriptive disclosure which is by no means limiting in anyway whatsoever. The present invention is elucidated in more detail belowusing examples. Alternative embodiments of the present invention areobtainable analogously.

EXAMPLES

For carrying out the examples and the determination of the respectiveparameters, the following basic assumptions were used, based on theC_(n)/C_(2n) system where n=5.

The degree of conversion Xi1 and Xi2 were calculated by the followingcalculation method:

${{Xi}\; 1} = \frac{\begin{matrix}{{\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} n} - {{pentanal}\mspace{14mu}{reactant}\mspace{14mu}{input}} -} \\{{\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} n} - {{pentanal}\mspace{14mu}{product}\mspace{20mu}{output}}}\end{matrix}}{{\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} n} - {{pentanal}\mspace{14mu}{reactant}\mspace{14mu}{input}}}$${{Xi}\; 2} = \frac{\begin{matrix}{{\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} 2} - {{methylbutanal}\mspace{14mu}{reactant}\mspace{14mu}{input}} -} \\{{\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} 2} - {{methylbutanal}\mspace{14mu}{product}\mspace{14mu}{output}}}\end{matrix}}{{\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} 2} - {{methylbutanal}\mspace{14mu}{reactant}\mspace{14mu}{input}}}$

The proportion of n-pentanal, based on the C5-aldehydes in the product(Sn1), was calculated by the following calculation method:

${{Sn}\; 1} = \frac{{\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} n} - {{pentanal}\mspace{14mu}{reactant}\mspace{14mu}{output}}}{\begin{matrix}{{\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} n} - {{pentanal}\mspace{14mu}{product}\mspace{14mu}{output}} +} \\{{\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} 2} - {{methylbutanal}\mspace{14mu}{product}\mspace{14mu}{output}}}\end{matrix}}$

The proportion of 2-propylheptenal, based on the unsaturatedC10-aldehydes in the product (Sn2), was calculated by the followingcalculation method:

${{Sn}\; 2} = \frac{{\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} 2} - {propylheptenal}}{\begin{matrix}{{\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} 2} - {propylheptenal} + {\%\mspace{14mu}{by}\mspace{14mu}{mass}\mspace{14mu} 4} -} \\{{propyl} - 4 - {methylhexenal}}\end{matrix}}$

The chemical compositions in the examples were determined by gaschromatography. For this purpose, a 7890A gas chromatograph from Agilentwas used with a flame ionization detector (FID). The column used was anHP-5 (5% phenylmethylsiloxane) 325° C. 30 m×320 μm×0.25 μm. Thefollowing temperature programme was applied for the analysis: 2 min at50° C., then to 150° C. at 10° C./min then at 40° C./min to 250° C. witha 10 min holding phase. Injection volumes 0.5 μl. Injector temperature250° C. nitrogen carrier gas at a flow rate of 105 ml/min and a split of50:1.

Example 1

In order to assess the separation of a particular isomer ratio prior tothe aldolization, simulation studies were conducted.

For the simulation, Aspen Plus V7.3 was used with the PSRK (predictiveSoave-Redlich-Kwong) method. The column is simulated as a Radfrac modeland is configured such that separation of the overhead product with ann-pentanal fraction of 30% up to 70% is possible. In particular, ann-pentanal fraction of 50% should be considered. In addition, the bottomproduct should contain an n-pentanal fraction of 95-100%. To achieve theisomer distribution, a column with 50 theoretical plates is used. Forthe calculations, the following starting concentration is considered,which is metered in in the liquid state. The results of the columnsimulation are also presented.

Bottoms Overhead Feed Mass fraction Mass fraction Mass fraction [—] [—][—] n-Butane 0.00065603 0 0.011 trans-2-Butene 0.00015467 0 0.003cis-2-Butene 0.00018928 0 0.003 2-Methylbutanal 0.03286881 0.004 0.483n-Pentanal 0.96607143 0.996 0.501

Example 2: Aldolization of n-Pentanal Including Condensation toα,β-Unsaturated C10 Aldehydes in a Stirred Reactor

The α,β-unsaturated C10 aldehydes were prepared in a stirred reactor.This reactor took the form of an extraction column having a volume of2.1 litres. The reactor was divided into ten mixing chambers and each ofthese mixing chambers was equipped with a 4-blade stirrer which weremounted on a common stirrer shaft. A catalyst phase was passed throughthe reactor in the circuit by a circuit pump. A 2% aqueous sodiumhydroxide solution was used as catalyst phase. The catalyst circuit was80 l/h in all experiments. The reactant comprised 98.3% by massn-pentanal, the remaining proportions being made up of secondarycomponents. The reactant was fed at 8 l/h continuously to the catalystcircuit just before the reactor inlet.

The biphasic mixture obtained at the reactor outlet was separated intoan organic product phase and a catalyst phase in a phase separationvessel.

The system was operated under a nitrogen atmosphere at a pressure of 4bar and, after three hours steady-state operation, the following resultswere determined.

Reaction conditions Stirrer speed rpm 2000 Temperature ° C. 130 Productcomposition n-Pentanal (% by mass) 4.9 2-Propylheptenal (% by mass) 91.3Remainder (incl. dissolved water) 3.8 Degree of conversion n-Pentanal0.95 Starting organic phase kg/h 5.8 Mass stream of pentanal kg/h 0.3Mass stream of 2-propylheptenal kg/h 5.8

Example 3: Aldolization of n-Pentanal and 2-Methylbutanal IncludingCondensation to α,β-Unsaturated C10 Aldehydes in a Flow Tube

The α,β-unsaturated C10 aldehydes were prepared in a three meter lengthDN15 tube having an internal diameter of 17.3 mm. This tube had a volumeof 6.8 litres. Circa 50% of the total volume was filled with staticmixers with a channel diameter of 2 mm. The mixing elements are formedfrom serrated lamellae which form open crossing channels. The channelsare arranged in the tube at a distance of one mixing length offset by90° from one another. With the aid of a pump, a continuous circulationof a catalyst phase of 80 l/h was established through this tube. A 2.1%aqueous sodium hydroxide solution was used as catalyst phase.

The reactant comprised 98.7% by mass n-pentanal, the remainingproportions up to 100% being composed of secondary components. Thereactant was fed continuously at 8 l/h to the catalyst circuit brieflybefore the start of the static mixers.

The biphasic mixture obtained at the reactor outlet was separated intoan organic product phase and a catalyst phase in a phase separationvessel.

The system was operated under a nitrogen atmosphere at a pressure of 4bar and, after three hours steady-state operation, the following resultswere determined.

Reaction conditions Temperature ° C. 130 Product composition n-Pentanal(% by mass) 2.9 2-Propylheptenal (% by mass) 93.3 Remainder (incl.dissolved water) 2.8 Degree of conversion of n-pentanal (Xi1) 0.97

Example 4

The reactant produced from example 3 was mixed with a C5 aldehydemixture consisting of 50% by mass n-pentanal and 50% by mass2-methylbutanal in such a way that, subsequently, approx. 7.3% of the C5aldehyde mixture and 92.7% of the aldol condensation product are presentin the feed mass.

This mixture was then subjected to hydrogenation. For the hydrogenation,a circulation system analogous to DE102009045718A1 example 1 was used.Analogous thereto, 105 g of catalyst were used composed of Cu (6% bymass)/Ni (3.1% by mass)/Cr (0.6% by mass) on Al2O3 as strand extrudateof 1.5 mm diameter and a length of 3-5 mm. The reaction conditions were180° C. and 25 bar absolute. The reactant feed was 100 ml/h at acirculation rate of 40 l/h and an offgas rate of 60 Nl/h.

7.3% C5-Aldehyde/92.7% aldolization product Composition Feed Productn-Pentanal (% by mass) 6.3 0.1 2-Methylbutanal (% by mass) 3.7 0.0*2-Propylheptenal (% by mass) 87.3 0.9 4-Propyl-4-methylhexanal (% bymass) 0.0* 0.0* n-Pentanol (% by mass) 0.0* 6.2 2-Methylbutanol (% bymass) 0.0* 3.6 2-Propylheptanol (% by mass) 0.0* 85.64-Propyl-4-methylhexanol (% by mass) 0.0* 3.6 Remainder 2.7 3.6n-Pentanol proportion based on the 0.63 C5-alcohols in the product2-Propylheptanol proportion based 1.0 on the C10- alcohols in theproduct *below detection limit

Example 5

For assessment of the purification of the product stream from thehydrogenation, simulation studies were conducted. For this purpose, aproduct stream consisting of C10 and C5 alcohols is separated intoindividual fractions according to FIG. 2. Used for this purpose wasAspen Plus V7.3 using the PSRK (predictive Soave-Redlich-Kwong) method.The columns are simulated as Radfrac models and the columns areconfigured such that separation of the products at a purity of ca. 99.9%is possible. To achieve the product qualities, four columns withdifferent specifications are provided.

Theoretical plates Column I 65 Column II 20 Column III 10 Column IV 55

By adding water (in the feed of column I), the separation of low-boilersis favoured. The water therefore does not accumulate in the columns andan aqueous phase is formed; water is removed at the top of each columninto a decanter.

Product Product stream 1 stream 2 (Alcohol (Alcohol from from startingFeed α,β-aldehydes) aldehydes) 2-Propylheptenal (% by mass) 0.9 0 0n-Pentanol (% by mass) 2.8 0 55.5 2-Methylbutanol (% by mass) 2.8 0 44.42-Propylheptanol (% by mass) 87.5 95.4 0 2-Propyl-4-methylhexanol (% by4.2 4.6 0 mass) H₂O 1.7 0 0

Example 6

As an alternative to the separation using 4 columns, the separation maybe carried out with the aid of dividing wall columns (likewise simulatedusing Aspen Plus V7.3, PSRK and Radfrac). For example, if column 2 and 3are replaced by a 31 stage dividing wall column, the alcohol of thestarting aldehydes may be drawn off as middle fraction.

The dividing wall extends in this case across 14 of the 31 plates. Theproduct is discharged on the 15th stage. The vapour stream impinging onthe dividing wall from below is fed in equal portions to the two columnsegments, whereas 75% of the liquid stream is passed to the product sideand 25% to the feed side.

If the overhead product of column 1 is passed to the dividing wallcolumn, the following product distribution arises:

Product (sidestream Feed to the dividing of the dividing wall columnwall column) H₂O (% by mass) 7.4 0 n-Pentanol (% by mass) 39.3 66.92-Methylbutanol (% by mass) 39.5 33.1 2-Propylheptanol (% by mass) 0 02-Propyl-4-methylhexanol (% by 0.6 0 mass) 2-Propylheptenal (% by mass)13.2 0

The results show that control of the amounts of C_(n) alcohol and C_(2n)alcohol with the procedure described is possible and the isomerdistribution of C_(n) can also be controlled in a corresponding manner.

LIST OF REFERENCE SYMBOLS

-   1 Hydroformylation product-   1 a Stream having a higher proportion of linear aldehydes than the    hydroformylation product-   1 b Stream having a higher proportion of branched aldehydes than the    hydroformylation product-   2 Mixture of aldol condensation product and stream having a higher    proportion of branched aldehydes than the hydroformylation product-   3 Hydrogenation product (for example where n=5 largely water,    butane, butene, C₅-aldehydes, 2-methylbutanol, pentanol, nonane,    α,β-unsaturated C₁₀ aldehydes, C₁₀-aldehydes, α,β-unsaturated    C₁₀-alcohols, C₁₀-alcohols, C10-oligomers having more than 10 carbon    atoms)-   4 C_(n)-alcohol (for example where n=5 largely 2-methylbutanol,    pentanol)-   5 C_(2n)-alcohol (for example where n=5 largely C₁₀-alcohols)-   6 Low-boiler stream depleted in C₁₀-alcohol with proportions of    heterogeneous water (for example where n=5 largely water    (heterogeneous), butane, butene, C₅-aldehydes, 2-methylbutanol,    pentanol, nonane, α,β-unsaturated C₁₀ aldehydes, C₁₀-aldehydes,    α,β-unsaturated C₁₀-alcohols)-   7 Aqueous phase-   8 Organic phase depleted in C₁₀-alcohol with proportions of    homogeneous water (for example where n=5 largely water    (homogeneous), butane, butene, C₅-aldehydes, 2-methylbutanol,    pentanol, nonane, α,β-unsaturated C₁₀ aldehydes, C₁₀-aldehydes,    α,β-unsaturated C₁₀-alcohols)-   9 Low-boiler stream (for example where n=5 largely water    (homogeneous), butane, butene, C₅-aldehydes, 2-methylbutanol,    pentanol, nonane)-   10 Organic phase with homogeneous water (for example where n=5    largely water (homogeneous), butane, butene, C₅-aldehydes,    2-methylbutanol, pentanol, nonane)-   11 Aqueous phase-   12 High-boiler stream (for example where n=5 largely    2-methylbutanol, pentanol, α,β-unsaturated C₁₀ aldehydes,    C₁₀-aldehydes, α,β-unsaturated C₁₀-alcohols)-   14 High-boiler stream (for example where n=5 largely α,β-unsaturated    C₁₀ aldehydes, C₁₀-aldehydes, α,β-unsaturated C₁₀-alcohols)-   15 High-boiler stream (for example where n=5 largely C₁₀-alcohols,    C10+-oligomers having more than 10 carbon atoms)-   18 High-boiler stream (for example where n=5 largely C10+-oligomers    having more than 10 carbon atoms)-   19 Return stream

The invention claimed is:
 1. A method for preparing saturated C_(n)- andC_(2n)-alcohols where n=4, 5 and 6, the method comprising the methodsteps of a) providing a mixture of isomeric C_(n)-aldehydes comprisingunbranched aldehydes, wherein the proportion of unbranched aldehydes isat least 20% by weight, based on the C_(n)-aldehydes, wherein theC_(n)-aldehydes were prepared by hydroformylation of isomeric olefinshaving 3 to 5 carbon atoms with synthesis gas in the presence of ahydroformylation catalyst to form the aldehydes specified, and whereinthe proportion of unbranched aldehydes is from 40 to 99.5% by weight,based on the C_(n)-aldehydes, wherein the hydroformylation comprises acatalyst system comprising rhodium as central atom and is complexed withthe ligand (1)

and an organic amine of formula (2)

in which Ra, Rb, Rc, Rd, Re and Rf represent identical or differenthydrocarbon radicals which may also be bonded to one another, b)carrying out a distillation for the at least partial separation of theisomeric C_(n) aldehydes into a first stream having a higher proportionof linear aldehydes than the mixture provided in a) and into a secondstream having a higher proportion of branched aldehydes than the mixtureprovided in a), c) carrying out an aldol condensation in a tubularreactor of the aldehydes present in the first stream having a higherproportion of linear aldehydes than the mixture provided in a) to obtaina mixture of C_(n)- and α,β-unsaturated C_(2n)-aldehydes wherein thetubular reactor comprises a mixing module which disperses the reactantaldehyde into droplets having an average diameter (Sauter diameter) of0.2 mm to 2 mm in a process liquor comprising aqueous sodium hydroxidesolution and sodium salts of carboxylic acids and has a sodium contentof 0.6 to 1.75%, d) mixing the mixture of C_(n)- and α,β-unsaturatedC_(2n)-aldehydes obtained in c) with the second stream, provided in b),having a higher proportion of branched C_(n) aldehydes than the mixtureprovided in a), e) hydrogenating the mixture of C_(n)- andα,β-unsaturated C_(2n)-aldehydes and C_(n)-aldehydes obtained in d) withhydrogen to obtain a mixture of saturated C_(n) and C_(2n)-alcohols, andf) separating the mixture of C_(n) and C_(2n)-alcohols.
 2. The methodaccording to claim 1, wherein the ligand (1) is3,3′-di-tert-butyl-5,5′-dimethoxy-[1,1′-biphenyl]-2,2′-diyltetrakis(2,4-dimethylphenyl)bis(phosphite).3. The method according to claim 2, wherein the organic amine comprisesat least one 2,2,6,6-tetramethylpiperidine


4. The method according to claim 1, wherein the aldol condensation instep a) is carried out in the presence of aqueous sodium hydroxidesolution, and wherein the proportion of unbranched aldehydes is from 95to 99.5% by weight, based on the C_(n)-aldehydes.
 5. The methodaccording to claim 1, wherein the process liquor has a pH in the rangefrom 12.5 to 13.5.
 6. The method according to claim 1, wherein the aldolcondensation of the C_(n)-aldehydes according to step a) is carried outin a temperature range from 100 to 150° C.
 7. The method according toclaim 1, wherein a reaction pressure in the tubular reactor during thealdol condensation of the C_(n)-aldehydes according to step a) is in arange from 0.2 to 1.0 MPa.
 8. The method according to claim 1, whereinthe hydrogenation according to step b) is carried out in a temperaturerange from 170° C. to 200° C. at a pressure of 15*10⁵ Pa to 30*10⁵ Paover a supported catalyst which contains at least nickel and copper asactive components.
 9. The method according to claim 1, wherein thehydrogenation according to step b) is carried out with hydrogen in apressure range from 5 to 100 bar and the hydrogenation temperatures arebetween 120 and 220° C.
 10. The method according to claim 1 wherein n=5.11. The method according to claim 2, wherein the aldol condensation instep a) is carried out in the presence of aqueous sodium hydroxidesolution.
 12. The method according to claim 3, wherein the aldolcondensation in step a) is carried out in the presence of aqueous sodiumhydroxide solution.
 13. The method according to claim 2, wherein theprocess liquor has a sodium content of 1.1 to 1.20% by mass and a pH inthe range from 12.5 to 13.5.
 14. The method according to claim 3,wherein the process liquor has a sodium content of 1.1 to 1.20% by massand a pH in the range from 12.5 to 13.5.
 15. The method according toclaim 2, wherein the aldol condensation of the C_(n)-aldehydes accordingto step a) is carried out in a temperature range from 100 to 150° C. 16.The method according to claim 3, wherein the aldol condensation of theC_(n)-aldehydes according to step a) is carried out in a temperaturerange from 100 to 150° C.
 17. The method according to claim 2, wherein areaction pressure in the tubular reactor during the aldol condensationof the C_(n)-aldehydes according to step a) is in a range from 0.2 to1.0 MPa.
 18. The method according to claim 2, wherein the hydrogenationaccording to step b) is carried out in a temperature range from 170° C.to 200° C. at a pressure of 15*10⁵ Pa to 30*10⁵ Pa over a supportedcatalyst which contains at least nickel and copper as active components.19. The method according to claim 1, wherein the hydrogenation accordingto step b) is carried out with hydrogen in a pressure range from 5 to100 bar and the hydrogenation temperatures are between 120 and 220° C.20. The method according to claim 2, wherein n=5.